As a connection plate for connecting longitudinal ends of elongated plates to make the elongated plates continue in the lengthwise direction, there have been a method of a type respectively inserting, from two directions, ends of elongated plates into two side grooves of a connection plate in the form of an H-shape facing side to establish the connection and a sandwich method of a type using abutting plates disposed onto the both sides of the elongated plates at the connection positions to hold the elongated plates. However, the conventional methods involve entering of rain occuring at the contact surface between the end of the elongated plates and the connection plate due to capillary phenomenon. Therefore, complete weathering (interruption and prevention of rain) cannot be realized.